1. Field of the Invention
The invention relates to a heating device and a heating method for a blow molding machine.
2. Description of the Prior Art
Blow molding machines, or also stretch blow molding machines, for producing containers are used particularly in the beverage industry. Containers are particularly bottles, which are produced from preforms (parison) made of plastic material. For this, in such blow molding machines, the preforms are initially heated in a heating device to a temperature at which they are deformable, the so-called deforming temperature. Subsequently, the heated preforms are shaped into the form of the desired finished container in a blow molding device by blowing a gaseous medium therein. In stretch blow molding machines, the containers are stretched further with a stretching rod.
In the heating device, the preforms are transported on a transport way along heating modules. Herein, the preforms are held at their mouth piece by a mandrel, which is seated in rotatable manner in a chain link. Further, several chain links with the mandrels seated therein are connected with each other such that the chain links form an endless revolving chain and therewith the transport way.
The heating modules are arranged externally besides the transport way and supply heat to the preforms via infrared radiation (IR-radiation). The infrared radiation is in addition reflected by reflectors arranged besides the transport way and under the transport way or under the bottom of the preforms. In this way, the infrared radiation can be effectively used for the heating of the preforms.
In presently used heating devices, a universal or all-purpose setting of the heating modules is selected with which the majority of the preforms to be heated with the heating device can be worked. In case the blow molding machine shall produce containers having different container sizes, for example bottles with a volumetric capacity of maximal 0.5 liter, 1.0 liter or 1.5 liter, the heating device also has to heat preforms having different sizes. In the event of using a universal setting of the heating modules for the preforms having different sizes, the same energy amount is consumed for heating all of the preforms having different sizes. Thus, currently used heating devices have especially when heating shorter preforms inferior power efficiency as compared to the heating of longer preforms. At least the power efficiency in heating shorter preforms is therefore not optimal.
DE 60 2005 003 970 T2 (also published as US 2008/0102148 and now U.S. Pat. No. 7,798,800) discloses a method and a device for heating thermoplastic preforms, in which two holders can each be used for holding either a heat source for heating the preforms or a reflector for reflecting heat radiation of the heat source. The selection, whether at one of the two holders is to be held a heat source or a reflector is made by a user from case to case, wherein the user takes into account the size of the preform to be heated by the device. As the case may be, the space settable between the preform and the reflector is not optimal for the heating of the preform, since the holders are only present at predetermined locations. In addition, a changeover time for changing over the device from heating a longer preform to heating a shorter preform or vice versa is not insignificant short.
A suboptimal power efficiency of machines is indefensible under environmental considerations. Furthermore, for an operator of a heating device or of a blow molding machine, steady increasing energy costs result in increasing operational costs which should be reduced.